Explosives



i E g Unite States Patent EXPLOSIVES Thomas F. McDonnell, Collinsville, 111., and Ralph E. Coffee, Berkeley, Mo., assignors to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation of Virginia No Drawing. Application December 2, 1955 Serial No. 550,758

5 Claims. (Cl. s2- 20 This invention relates to explosives and more particularly to an improved process for the manufacture of smokeless powder. One of the prime requisites in smokeless powder propellent grains is their free flowing characteristics. If the powder grains are not free flowing or if they have any tendency whatsoever to adhere to one another or to apparatus used in loading ammunition, the powder is exceeding difficult to handle and there is no assurance that the proper powder charge will be deposited in each cartridge case. Furthermore, any tendency on the part of the powder to be tacky will have a deleterious eflect on its gravimetric density and the cohesion of the powder grains will tend toward the formation of voids in the powder charge and in severe instances this may be so great as to render the powder practically useless.

Most of the propellent powders produced by the conventional methods are free flowing but in some instances when a particular ballistic level is desired it is necessary 1 to use more than the normalamount of modifier in the powder and such powder grains very often tend to have a surface layer of tacky modifier that is not completely incorporated into the grain. Such a relatively large amount of modifier is required in particular applications for the proper ballistic effects, but it leads to considerable handling and loading difficulties due to the inherent tendency of such powder to have a tacky surface. Similar undesirable characteristics are encountered when for some reason or another the modifier applied to the surface of the grain fails to be completely incorporated into the body of the grain, or the grains are contaminated with a foreign substance such as grease or oil. Furthermore, such powder has a very short storage life, for after standing for a matter of weeks it has a tendency to set up or consolidate into a solid mass, which renders subsequent handling very difficult if not impossible.

In order to render such tacky powder more suitable for use it is the common practice to remove the modifier from the powder surface by treatment with a solvent for the material on the surface of the grain. Such a process is very difficult to control, greatly increases the cost of the powder and results in the removal of an appreciable portion of the modifier and consequently involves an unpredictable variation of the ballistic properties of the powder.

It is therefore an object of this invention to provide a process of preparing free flowing powder without affecting the ballistic properties of the powder. It is also an object of this invention to provide a process of increasing the gravimetric density of propellent powder grainsi It is another object of this invention to provide more latitude in the composition of free flowing powders. -A further object of this invention is to provide a novel method of treating propellent powder grains. Still another object of this invention is to provide a method of improving the storing qualities of propellent powder grains.

Cit

It has been found that these and other objects may be accomplished in accordance with this invention,"gen-..

Patented Nov. 11, 1958 erally speaking, by transferring the tacky substance from the surface of the grain to another solid material. More specifically, this invention contemplates the removal of the tacky substance on the surface of the gIainby'con-J tacting the grains while suspended in an aqueous medium with a solid material having a greater afilnity for the tacky substance than does the surface of the powder grain. This invention contemplates the removal of such tacky or gummy substances from the surface of powder grains by suspending the grainsin anaqueous mediumin which small particles of a solid substance capable 'Ofl'? moving the objectionable material from the grain surface are also suspended. This process is dependent upon the. greataflinity of finely divided suspended'rnaterial; for the tacky substance on the surface of the powder grain.

This transfer of the tacky material from the surface.

grain is believed tobe primarily dependent upon the adsorptive properties of the finely divided ma'terialand thus inmost instances the material is believed tobe held by, adhesive forces on the surface of the treating material:

However, when the treating material or removingagent;

is of a porous nature, someabsorption is also undoubt edly involved and the material removed from the surface of the grain is then held within the pores of the treating agent, probably bymeans of capillary action, In those.

cases where a finely divided porous material isused in,

of the tacky material from the powder grain; Thus, thepresent invention is not limited to any-particulartheog retical consideration but encompasses any .process in which the solidmaterial"iiiaqueous suspension -is com tacted with the powder grains also in suspension so as,

to reiriove the tacky material regardless of the particular mechanics involved.

The process is carried out in a vessel ofsuitablesize provided with an agitation system capable of keeping-the; powder grains and; adsorptive material in suspension and preferably substantially uniformly distributed throughoutthe aqueous medium. The invention can be utilized in.

treating powder made by any of the commercial proc-' esses. It ishowever admirably suited as an adjunctto,

the process of deterrent coating powder grains by. contacting the grains with a modifier while bothare suspended in water, as set forth in U. S. Patent No. 1,955,927 to McBride, as well as the process of making globular grains of powder by removal of the solvent from pow der base lacquer droplets while suspended in, a non-so1-.

vent mediurmas described in U. S. Patent 'No. 2,027,114;

to Olsen, Tibbets and Kerone. While in most instances it has been found more convenient to add the powder; grains to an agitated suspension of the adsorptive material, this inventionis not limited to any particular se: quence of introducing the constituents of the process into the apparatus.

up to about C. When the powder being treatedhas been provided with a surface coating of a modifier tern,--

peratures above about 80 0. should not be used, ;for-

heating above this value induces migration of the modifier that are water-insoluble and stable and inert toward the .jngredients while suspended in the aqueoussystem withi The process is most conveniently car-l ried out at room temperature. However, in some eases,-. advantageous results are achieved by usingtemperatures,

Y rating and washing the 3 or without the assistance of a surface active agent. Materials particularly well suited for the process of this invention because of their high degree of efficiency include diatomaceous earth, celite, precipitated chalk, alumina, magnesium carbonate, activated charcoal, carbdnblack, silica, and the like. When the material is suspended'in water, it normally retains its original physical characteristics and is present in the form of solid discrete particles. Its efiiciency is a function of its particle size 'and more eflicient operation is insured when the material is in a state of fine subdivision. The treating material must be of such fineness as to pass through a 200 mesh screen,-i.- e., corresponding to a particle size not greaterthan 74 micronsf Any particles coarser than those which would pass'through B72700 mesh screen are very ineffective, andtherefore it becomes necessary to have substantially all of the material pass through a 200 mesh- 'screen. In fact, a higher degree of fineness is preferred and whenever possible materials having a particle size range between about 1 and about 50 microns are employed.

"The'amou'ntof removing agent used in accordance with the process of this invention can vary within wide limits'a'nd is generally dependent upon the particular type of agent used and also upon the nature of the material to beremoved from the surface of the grain. For example, as'lit'tle as one percent of carbon black based on the weight'of the powder being treated has. been found to: be effective and six percent activated charcoal is equally effective but up to fifty percent or more chalk rn'ay' befrequired to obtain satisfactory powder in some instances.

-I'n'carrying out this invention the powder grains being treated should be suspended in a suflicient amount of aqueous medium so as to give them relatively free movement therein, and the ratio of the powder grains to the water must be low enough to prevent undue crowding of the powder grains. It will, thus, be appreciated that the ratio of powder grains to water may vary considerably and will' depend to a certain extent upon the type of powder being treated, the size of the powder grains, the typeof material employed in treating the grains, and the characteristics of the material being removed from the surface of the grain. In most instances, however, it has been found preferable to suspend the powder grains in fromfabout'2 /2 to 5 times their weight of water. It willf-be; readily appreciated that the invention can be carriedout in systems in which the powder to water'ratio is less than 21621 or greater than 5:1, but operation within these limits leads to greater efiiciency and economy in the process.

After the tacky material has been removed from the surface of the powder grains it is necessary to remove the powder grains from the absorptive and/ or adsorptive material. This in'ay be accomplished in a numbe'rfof ways-and different separation methods may be found more appropriate when different adsorptive agents are employed. In most instances, it has been found preferable to separate thepowder from the material by permitting the powder grains to settle to the bottom of the aqueous medium and then decanting the water and suspended material from the powder. This process is normally followed by washing with clear water, followed .by one or more decantations. Alternate methods for sepapowder from the treating materials are equally effective. Thus, the separation can be effected by passing the water containing the powder grainsand treating material through a screen having openings large enough to allow passage of the treating material but'small enough to retain the powder grains. In order to further explain and clarify this invention, following is a preferred embodiment thereof in which propellent powder having a tacky or gummy surface was rendered free flowing. Throughout this embodiment, proportions of materials, are expressed in parts by weight.

The powder forming the base material for this embodiment was a double base globular powder of the type de-l scribed in, U. S. Patent No. 2,027,114 and having a nominal composition of 82% nitrocellulose, 15% nitroglycerine and 3% diphenyl phthalate, the size of the grain varying between 0.009" and 0.013". The diphenyl phthalate had been applied to the hardened powder grains by a conventional coating method but this deterrent had not penetrated deeply enough into the grain and a small portion remained on the grain surface. This condition caused the powder to be sticky, incapable of fiowarms' ing freely and wholly unsuitable for use in small ammunition.

In carrying out this preferred embodiment, 40 parts ofwater were introduced into a still equipped with'agitw' tional means capable of'keeping the material to be added in suspension and thoroughly agitated. One part of precipitated chalk wasthen added; to the water and the agitation was continued to form a homogeneous suspension of the chalk in the water. After the chalk had been. a

At the end of this time the removal of the surface diphenyl phthalate had been completed and the agitation. of the system was stopped causing the powder grains to 7 settle to the bottom of the still, the chalk and water. 'i

slurry was then decanted from the powder, the still refilled with fresh water, agitated for a few minutes and again decanted. This washing and decantation' operation was repeated two more times and the powder was then completely separated from the chalk. The powder was then removed from the still, placed in shallow trays and exposed to a gentle current of hot air until dry. The resulting powder possessed none of the gummy or tacky characteristics of the powder originally submitted to this process and it was free flowing and entirely satisfactory for subsequent use.

Aside from the economics involved in carrying out the process of this invention, another marked advantage of the process is that it affects no significant change in the composition of the powder, and the ballistic properties of the powder are thus not appreciably changed. In order to illustrate the maintenance of the desired ballistic properties of powder treated in accordance with this invention, a powder in its original sticky condition was loaded into .22 caliber long rifle cartridge cases provided a with standard 40 grain molded lead bullets. These cartridges were fired and the ballistic characteristics were compared with identical .22 caliber cartridges loaded with the-same powder after treatment in accordance with this invention. The results of these firing tests are set forth in the following table.

From this data it is evident that the gravimetric density of the treated powder which is a measure of the free flowing ability of the powder has been appreciably increased; whereas, the ballistic level of the powder was not sacrificed, for the pressure and velocity of cartridges loaded with the. treated and untreated powder are within the range of experimental error.

Fromrthe abovedescription it is clear that this invention accomplishes its objects and provides a novel process for-removi g acky material from the surface of powder ains withotit'altering its ballistic properties and thus obviates the necessity of comprising between desired chemical composition and optimum ballistic properties.

Having now described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A method of transferring tacky substance from the surface of propellent powder grains to a solid adsorptive material selected from the group consisting of diatomaceous earth, celite, precipitated chalk, alumina, magnesium carbonate, activated charcoal, carbon black, and silica and being sufi'iciently fine to pass through a 200 mesh screen which comprises suspending the powder grains and at least 1 percent of the adsorptive material in an agitated aqueous medium, maintaining the agitation of the aqueous medium to keep the powder grains in suspension and subsequently decanting and washing the powder grains.

2. A method of removing tacky material from the surface of propellent powder grains comprising adding the powder grains to an agitated aqueous medium containing at least 1 percent of discrete solid particles of suspended adsorptive material selected from the group consisting of diatomaceous earth, celite, precipitated chalk, alumina, magnesium carbonate, activated charcoal, carbon black, and silica, said particles having a fineness of at least 200 mesh, maintaining the agitation of the aqueous medium to keep the powder grains in suspension, and separating the powder grains from the water suspension of the particulate material.

3. A method of removing tacky material from the surface of propellent powder grains comprising adding the powder grains to an agitated aqueous medium containing at least 1 percent of discrete solid particles of suspended adsorptive material selected from the group consisting of diatomaceous earth, celite, precipitated chalk, alumina,

magnesium carbonate, activated charcoal, carbon black, and silica, said particles having a particle size range between about 1 micron and about 50 microns, maintaining the agitation of the aqueous medium to keep the powder grains in suspension, and separating the powder grains from the water suspension of the particulate material.

4. A method of removing tacky material from the surface of propellent powder grains comprising suspending the powder grains in from about 2 /2 to about 5 times their weight of water together with between about 1 percent to about 50 percent of their weight of a solid adsorptive material selected from the group consisting of diatomaceous earth, celite, precipitated chalk, alumina, magnesium carbonate, activated charcoal, carbon black, and silica, and separating the powder grains from the water suspension of the particulate material.

5. A method of removing tacky material from the surface of propellent powder grains comprising suspending about 10 parts by weight of the powder grains in about parts by weight of agitated water having suspended therein about 1 part by weight of precipitated chalk, continuing the agitation for approximately 15 minutes and subsequently decanting and washing the powder grains.

Uses and Applications of Chemicals and Related Materials, vols. I and II, by Gregory, Reinhold Publ. Co., N. Y., 1939 (Vol.1); 1944 (vol. II). 

1. A METHOD OF TRANSFERRING TACKY SUBSTANCE FROM THE SURFACE OF PROPELLENT POWDER GRAINS TO A SOLID ADSORPTIVE MATERIAL SELECTED FROM THE GROUP CONSISTING OF DIATOMACEOUS EARTH, CELITE, PRECIPITATED CHALK, ALUMINA, MAGNESIUM CARBONATE, ACTIVATED CHARCOAL, CARBON BLACK, AND SILICA AND BEING SUFFICIENTLY FINE TO PASS THROUGH A 200 MESH SCREEN WHICH COMPRISES SUSPENDING THE POWDER GRAINS AND AT LEAST 1 PERCENT OF THE ADSORPTIVE MATERIAL IN AN AGITATED AQUEOUS MEDIUM, MAINTAING THE AGITATION OF THE AQUEOUS MEDIUM TO KEEP THE POWDER GRAINS IN SUSPENSION AND SUBSEQUENTLY DECANTING AND WASHING THE POWDER GRAINS. 